1. Field of the Invention
The present invention relates to a wafer processing system.
2. Description of the Related Art
Conventional wafer processing systems include a plurality of manufacturing units used to perform different wafer processing manufacturing operations. In particular, these manufacturing operations include processes in which layers are applied to the wafers. These include, for example, sputtering processes, vapor deposition processes, C.D. processes and thermal oxidation processes. Other manufacturing steps for processing wafers include, for example, etching processes, wet chemical processes, diffusion processes as well as different cleaning processes such as, for example, CAMP (Chemical Mechanical Polishing). One or more manufacturing units are provided for each of the corresponding manufacturing operations. In addition, separate measuring units where the quality of wafer processing can be checked are provided. All manufacturing operations performed in the manufacturing units are preferably checked using such measuring units.
The entire manufacturing process is subject to strict cleanliness requirements, so that the manufacturing units and measuring units are arranged in a clean room or a system of clean rooms.
The wafers are supplied to the individual manufacturing and measuring units in predetermined lot sizes via a transport system. For this purpose, the wafers are transported in transport containers, which may be designed as cartridges, for example. After the wafers have been processed in the manufacturing and measuring units, they are also removed by the transport system.
The transport system has a conveyor system, which may be designed as a roller conveyor, for example. In addition, the transport system may have a buffer system with a plurality of buffer stations for storing the transport containers with the wafers. The storage devices are preferably designed as stockers.
One disadvantage of this is that inspecting the quality of wafer processing is very time consuming and also requires a great structural complexity. After the wafers have been processed in a manufacturing unit, they must be sent to the corresponding measuring unit via the transport system, which often also requires temporary storage of the wafers. The measuring unit itself requires a considerable structural complexity. First, devices to receive the wafers from the transport system must be provided at the measuring unit, and then after the measurement has been performed, devices for delivering the wafers to the transport system must also be provided. In addition, the measuring unit has inspection devices where the quality of wafer processing is checked. Another disadvantage is that a considerable amount of space is required for the measuring units, so a large amount of floor area is required for the system accordingly. Since clean rooms themselves are also extremely expensive, this means a considerable cost factor for such systems.
One disadvantage of such measuring units is that measurements performed there permit only an indirect and incomplete conclusion regarding the quality of the manufacturing operation conducted in the manufacturing unit. For example, the layer thickness of wafers is typically determined in measuring units assigned to manufacturing units for applying layers to the wafers. To guarantee a sufficiently accurate measurement of layer thickness, the equipment required in the corresponding measuring unit is considerable.
Even if the layer thickness on the wafer can be determined very accurately, the source of error in the manufacturing process can be determined only inaccurately and incompletely when a deviation in the measured layer thickness from the predetermined set point is found. If the respective manufacturing unit is formed by a CVD installation for vapor phase deposition of silicon on the wafer, for example, then predetermined pressure and temperature conditions must prevail in the corresponding manufacturing unit, for example. However, if an erroneous layer thickness is found in the measuring unit, this does not permit a clear inference as to whether the correct temperature and pressure conditions have been selected for the manufacturing unit.
An object of the present invention is to determine the quality of wafer processing as accurately and completely as possible with the least possible expense.
According to the present invention, to check the quality of wafer processing of one or more manufacturing operations conducted in a manufacturing unit, measuring devices are used in the manufacturing unit for determining process parameters.
The process data thus obtained from the measuring devices is compiled in a computing unit assigned to the manufacturing unit. Finally, characteristic quantities for evaluating the quality of wafer processing are derived from this process data.
According to the present invention, measuring devices which are usually already provided for monitoring the manufacturing operations in the individual manufacturing units are also used at the same time to check the quality of wafer processing.
This makes use of the circumstance that the result of processing a wafer in a manufacturing unit can be determined unambiguously by checking the process data generated in the manufacturing unit by using the measuring devices.
Since the characteristic quantities for evaluating the processing quality are obtained directly from the process data of the corresponding manufacturing unit determined by using the measurement devices, this makes it possible not only to determine whether a wafer has been processed correctly or defectively, but also in the event of a defect, to determine exactly the cause of the defect from the individual characteristic quantities. Depending on which of the characteristic quantities deviates from a setpoint or has other irregularities, such as a great scattering about a mean, it is possible to deduce the corresponding faulty process parameters from it. Consequently, not only is it possible to determine the quality of wafer processing through determination of the characteristic quantities according to the present invention, but also conclusions can be reliably drawn regarding possible errors in processing the wafers.
One advantage of the system according to the present invention is that the quality of processing of manufacturing steps can be checked in a manufacturing unit itself. Consequently, separate measuring units are no longer needed for such manufacturing units. This leads to considerable savings in terms of equipment and ultimately also of cost-intensive clean room space. Furthermore, wafer throughput time through the system is greatly shortened, because after the wafers have been processed in a manufacturing unit, they need no longer be sent to a downstream measuring unit via the transport system.